[game] Walk controls (unbound)

game/main.ts

@@ -1,6 +1,8 @@
 import { cls, print, spr, use_texture } from "./graphics";
 import { load_texture } from "./assets";
-import { since_start, since_last_frame } from "./time";
+import { since_start } from "./time";
+import { btn, Button } from "./input";
+import { new_v2, vadd, vmul, vnorm } from "./vector";
 
 let bot_sprite: number | undefined = undefined;
 
@@ -14,7 +16,39 @@ export function init() {
   });
 }
 
-export function update() {}
+const friction = 0.6;
+let robo_vel = new_v2(0);
+let robo_pos = new_v2(10);
+
+export function update() {
+  // Acceleration from input
+  let a = new_v2(0);
+  if (btn(Button.Up)) {
+    a.y -= 1;
+  }
+  if (btn(Button.Down)) {
+    a.y += 1;
+  }
+  if (btn(Button.Left)) {
+    a.x -= 1;
+  }
+  if (btn(Button.Right)) {
+    a.x += 1;
+  }
+  vnorm(a);
+
+  // Friction
+  let v = vmul(robo_vel, friction);
+  v = vadd(v, a);
+
+  // Motion
+  let np = vadd(robo_pos, v);
+
+  // TODO: Collide.
+
+  robo_pos = np;
+  robo_vel = v;
+}
 
 export function draw() {
   cls(0.1, 0.2, 0.3);
@@ -22,8 +56,7 @@ export function draw() {
     // ...it gets resolved here?
     use_texture(bot_sprite);
 
-    let y = (since_start() * 10) % 240;
-    spr(10, y, 32, 32, 0, 0);
+    spr(robo_pos.x, robo_pos.y, 32, 32, 0, 0);
   }
   // print("FRAME TIME:", since_last_frame());
 }